The present invention relates to an electrophotographic photoreceptor, and an image forming method, as well as an image forming apparatus, employing said electrophotographic photoreceptor, and a processing cartridge.
In recent years, widely employed as electrophotographic photoreceptors, have been organic photoreceptors. Compared to other photoreceptors, organic photoreceptors exhibit advantages in that it is easy to develop materials which correspond to various types of exposure light sources ranging from visible light to infrared rays; it is possible to select materials which result in minimal environmental pollution; their production cost is lower, and the like. However, said organic photoreceptors exhibit disadvantages in that the mechanical strength is insufficient, and when producing numerous prints, the photoreceptor surface tends to be degraded or abraded.
Since electrical and mechanical external force is directly applied to the surface of electrophotographic receptors (hereinafter referred occasionally to as photoreceptors) upon employing charging means, developing means, transfer means, cleaning means, and the like, durability is required to counter such force.
Specifically required is durability to resist wear and abrasion of the photoreceptor surface due to friction, surface degradation due to active oxygen such as ozone, nitrogen oxides, and the like, which are generated during corona charging.
In order to overcome said drawbacks, techniques have been investigated in which a protective layer, exhibiting enhanced strength, is provided on the photoreceptor surface, and the like. For example, Japanese Patent Publication Open to Public Inspection No. 6-118681 discloses that silicone resins are employed as the protective layer of the photoreceptor. However, the transportability of generated carriers results in problems. As a result, particularly at the low humidity environment, which results in an increase in resistance, problems result in response properties. In the field of digital copiers, high image quality has been increasingly demanded, followed by the investigation of the image formation resulting in high resolution. However, the surface protective layer, which exhibits such insufficient response properties, results in diffusion of carriers and it, is impossible to obtain excellent electrostatic latent images.
In order to faithfully reproduce image information as electrostatic latent images, it is required that the electric potential contrast of an exposed area to an unexposed area is sufficiently limited. In order to realize said contrast, it is important to retard the diffusion of carriers from their generated sites to the charge surface. Nihon Gazo Gakkai Shi (Journal of Japan Image Society), Volume 39, No. 3, page 294-295 describes said diffusion as follows: when the ratio of D/xcexc increases, it is impossible to neglect the effects of the diffusion to an electrostatic latent image, wherein D is the diffusion constant of the charge transport layer, and xcexc is the drift mobility, while the thickness of the charge transport layer increases, the degradation of latent images increases. However, organic electrophotographic photoreceptors, which are commonly employed, result in a large decrease in the layer thickness due to the sliding of cleaning blades and the like. Accordingly, it has not been preferred to design the thickness of the photosensitive layers, such as a charge transport layer and the like, to be not more than 20 xcexcm because the durability of the resulting photoreceptor is further degraded.
From the view of the foregoing, investigations have been conducted on electrophotographic receptors which exhibit sufficient strength against the sliding of cleaning blades and the like, and provide sufficient electric potential contrast of the exposed area to an unexposed area in the low humidity environment, a high quality image forming method, and an image forming apparatus employing said electrophotographic photoreceptor, and the like.
It is an object of the present invention to overcome the aforementioned drawbacks, and to provide a photoreceptor which possesses high surface hardness, high wear resistance, and provides sufficient and consistent electrophotographic properties during repeated use, such as electric potential contrast of an exposed area to an unexposed area at a severe ambience such as high temperature and high humidity as well as low temperature and low humidity, and further, provides an image forming method as well as an image forming apparatus employing said photoreceptor, and a processing cartridge employed in said image forming apparatus.
The inventors of the present invention have conducted investigations to solve the problems described above. As a result, it was discovered that in a photoreceptor in which a hardenable resinous layer having high surface hardness, a decrease in the difference of ionization potential between said hardenable resinous layer and the underlying photosensitive layer, such as, for example, a charge transport layer, effectively retarded the diffusion of carriers of said photoreceptor. Namely, it was discovered that when the difference in ionization potential between said hardenable resinous layer and said transport layer was kept at not more than 0.4 eV and a response time of the total photoreceptor is kept at not more than 0.25 second, electrostatic latent images can be consistently resulting in excellent images.
The present invention and the embodiments thereof will now be described.
1. An electrophotographic photoreceptor comprises an electrically conductive support having thereon a photosensitive layer and a hardenable resinous layer, wherein a difference in ionization potential between said photosensitive layer and said hardenable resinous layer is not more than 0.4 eV, and a response time T10 defined below is not more than 0.25 second.
 less than Response Time T10 greater than 
When a photoreceptor charged at |600 V|xc2x120 V is subjected to a sufficient amount of light irradiation so that |200 V| or less results due to light decay, said response time T10 refers to the elapsed time during which the average of 10 electrical potentials between surface electric potential data adjacent to each other, which are measured at an interval of 10 milliseconds after light irradiation, reaches 10 V or less.
2. In the electrophotographic photoreceptor of described above, the photosensitive layer preferably comprises a charge generating layer and a charge transport layer, and a difference in ionization potential between said charge transport layer and said hardenable resinous layer is not more than 0.4 eV, and a response time T10 is not more than 0.25 second.
3. In the electrophotographic photoreceptor of described in 1. or 2. above, said hardenable resinous layer is preferably a siloxane based resinous layer which is obtained by allowing an organic silicon compound having a hydroxyl group or a hydrolyzable group to react with a compound represented by General Formula (1).
Bxe2x80x94(R1xe2x80x94ZH)mxe2x80x83xe2x80x83General Formula (1)
xe2x80x83wherein B represents a univalent or multivalent group comprising structural units having charge transportability, R1 represents a single bond or divalent alkylene group, Z represents an oxygen atom, a sulfur atom or NH, and m represents an integer of 1 to 4.
4. In the electrophotographic photoreceptor described in 3. above, Z in General Formula (1) is preferably an oxygen atom.
5. In the electrophotographic photoreceptor described in any one of in 1. through 4. above, said hardenable resinous layer is preferably a cross-linking structure containing siloxane based resinous layer exhibiting charge transportability.
6. In the electrophotographic photoreceptor described in 5. above, said siloxane based resinous layer preferably comprises the partial structure represented by the aforementioned General Formula (2).
Bxe2x80x94(R1xe2x80x94ZH)mxe2x80x83xe2x80x83General Formula (2)
xe2x80x83wherein B represents a univalent or multivalent group comprising structural units having charge transportability, R1 represents a single bond or divalent alkylene group, Z represents an oxygen atom, a sulfur atom or NH, and m represents an integer of 1 to 4.
7. In the electrophotographic photoreceptor described in any one of 1. through 6. above, said hardenable resinous layer preferably comprises colloidal silica or metal oxide particles.
8. The electrophotographic photoreceptor described in any one of 1. through 7. above, said hardenable resinous layer preferably comprises an antioxidant.
9. In the electrophotographic photoreceptor described in any one of 1. through 8. above, said hardenable resinous layer is preferably the protective layer of said electrophotographic photoreceptor.
10. In the electrophotographic photoreceptor described in 1. above, the total layer thickness of said photosensitive layer and said hardenable resinous layer is preferably not more than 15 xcexcm, and said response time T10 is preferably not more than 0.1 second.
11. An image forming method which comprises at least each process of charging, image exposure, development, and blade cleaning, and forms a latent image by employing an electrophotographic photoreceptor described in any one of 1. through 10. above as well as by employing a light beam having a spot area of not more than 2,000 xcexcm2 during said image exposure process.
12. The image forming method described in 11. above wherein the spot area of said light beam is preferably not more than 1,000 xcexcm2.
13. In the image forming method described in 11. above, the electrophotographic photoreceptor described in any one of 1. through 10. above is employed and the average particle diameter of a toner employed in said development process is preferably between 3 and 8 xcexcm.
14. In the image forming method described in 13. above wherein the ratio of toner having a shape coefficient of 1.0 to 1.6, is preferably at least 65 percent in terms of the number of particles.
15. In the image forming method described in 13. or 14. above, a latent image is formed preferably employing a light beam having a spot area of not more than 2,000 xcexcm2.
16. An image forming method which comprises at least each process of charging, image exposure, development, and blade cleaning, and forms an image by employing an electrophotographic photoreceptor described in any one of 1. through 10. above, so that time from said image exposure process to said development process is within 100 milliseconds.
17. An image forming apparatus which comprises at least each device of charging, image exposure, development, and blade cleaning, and forms a latent image by employing an electrophotographic photoreceptor described in any one of 1. through 10. above, as well as by employing a light beam having a spot area of 2,000 xcexcm2 in said image exposure device.
18. An image forming apparatus which comprises at least each device of charging, image exposure, development, and blade cleaning, and forms a latent image by employing an electrophotographic photoreceptor described in any one of 1. through 10. above, as well as by employing a toner having an average particle diameter of 3 to 8 xcexcm in said development device.
19. In an image forming apparatus described in 18. above wherein the ratio of a toner having a shape coefficient in the range of 1.0 to 1.6, is preferably at least 65 percent in terms of the number of particles of the toner.
20. In an image forming apparatus described in 18. or 19. above, a latent image is formed preferably employing a light beam having a spot area of not more than 2,000 xcexcm2 during the image exposure process.
21. An image forming apparatus which comprises at least each device of charging, image exposure, development, and blade cleaning, and forms an image by employing an electrophotographic photoreceptor described in any one of 1. through 10. above so that time from process by said image exposure device to process by said development device is within 100 milliseconds.
22. A processing cartridge which is employed in an image forming apparatus comprising at least device of charging, image exposure, development, and cleaning, and has an integral combination of the photoreceptor described in any one of 1 through 10. above with any one of a charging means, exposure means, a development means, and a cleaning means, and is designed to be freely mounted on and dismounted from said image forming apparatus.